The finding, however, is buffered with some reassurance. "I want to emphasize that lip cancer is rare," says Gary D. Friedman, MD, an emeritus researcher and former director of the Kaiser Permanente Northern California Division of Research. He led the study.

Lip cancer rarely spreads, he says. It is usually recognized early and treated promptly.

"I do not want to alarm people to the extent they are going to stop taking their medicine for blood pressure," he says. The study findings are not a reason to stop any medicines that make people more sensitive to the sun, he says.

The study is published online in the Archives of Internal Medicine.

Every year in the U.S., about 35,000 people are diagnosed with oral cancers, including lip cancers, according to the National Cancer Institute.

Blood Pressure Drugs & Lip Cancer: Study Details

In a previous study, Friedman had noticed an increase in lip cancers among people on certain high blood pressure medicines.

For this study, he evaluated the types of blood pressure prescriptions dispensed and lip cancers found in patients at Kaiser Permanente from 1994 until early 2008.

He focused only on lip cancers, Friedman says, because data on skin cancers was not available.

Friedman focused on five high blood pressure drugs or drug combinations that are commonly prescribed. Besides hydrochlorothiazide and lisinopril, they included: